High strength aluminum base alloy

ABSTRACT

A high strength aluminum base alloy having good wear resistance consisting essentially of silicon from 7 to 20 percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to 1.0 percent, copper from 3.5 to 6 percent, balance essentially aluminum, and processing same.

United States Patent [1 1 Sperry et al.

[ Oct. 16, 1973 HIGH STRENGTH ALUMINUM BASE ALLOY Inventors: Philip R.Sperry, North Haven;

Joseph Winter, New Haven; Michael J. Pryor, Woodbridge, all of Conn.

Olin Corporation, New Haven, Conn.

Filed: Nov. 24, 1972 Appl. No.: 309,134

Assignee:

US. Cl 75/142, 75/141, 148/3,

148/325, 148/159 Int. Cl. C22c 21/02 Field of Search 75/142, 141;148/32,

[56] References Cited UNITED STATES PATENTS 2,525,130 10/1950 Hall eta1. 75/142 Primary ExaminerRicharcl 0. Dean Atrorney-Robert H. Bachmanet a].

[57] ABSTRACT 11 Claims, No Drawings HIGH STRENGTH ALUMINUM BASE ALLOYBACKGROUND OF THE INVENTION Aluminum alloy castings having good physicalproperties especially high strength and wear resistance, have long beenneeded for a variety of reasonsfGenerally, aluminum casting alloyscurrently available have provided strength levels well below thoseobtainable with machined plates and billets, machine forging and wroughtassemblies.

US. Pat. No. 3,475,166 teaches a high strength aluminum casting alloyhaving good physical properties. This patent teaches an alloy havinggood elevated temperature properties which would be desirable fordesigning pistons or stressed engine parts with reduced weight. However,this material does not have adequate resistance to galling, scuffing, orwear.

Accordingly, it is a principal object of the present invention toprovide a new and improved aluminum base casting alloy having highstrength and wear resistance.

It is a further object of the present invention to provide an aluminumalloy as aforesaid which has good elevated temperature properties andalso good resistance to galling, scuffing or wear.

It is a particular object of the present invention to provide analuminum casting alloy as aforesaid which is useful in the design ofpistons or other highly stressed engine parts which operate at elevatedtemperatures. Further objects and advantages of the present-inventionwill appear hereinafter.

SUMMARY OF THE INVENTION In accordance with the-present invention it hasbeen found that the foregoing objects and advantages may be readilyobtained. The aluminum base alloy of the present invention consistsessentially of silicon from 7 to 20 percent, preferably from 7 to 12percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to 1.0.percent, copper from 3.5 to 6 percent, balance essentially aluminum.Naturally, numerous optional additives and conventional impurities maybe readily utilized as will be seen from the ensuing specification.

In accordance with the present invention, it has been found that thepresent alloys have good elevated temperature properties combined withgood resistance to galling, scuffing or wear. The addition of silicon inthe large amounts utilized herein has been found to provide wearresistance, surprisingly without detracting from the strength of thematrix.

Furthermore, it has been surprisingly found that the basic heattreatability of the alloy matrix is not affected by silicon additions inthe range of from 7 to 20 per-- cent, and in fact some tensile strengthincrease can be obtained. In addition to the foregoing, othersignificant advantages may be obtained in accordance with the alloy ofthe present invention. For example, Brinell hardness is surprisinglyhigh, indicating excellent wear resistance.

In addition, the present invention teaches a method of processing thealuminum base alloy set forth above.

' The method comprises casting the alloy in the temperature range ofl,250 to 1,500 F and aging the alloy in the temperature range of 300 to500 F for from one to 24 hours. Preferably a solution heat treatment isprovided after casting and before aging at a temperature of 850 to 975 Ffor from one to 40 hours, followed by quenching.

DETAILED DESCRIPTION As indicated hereinabove, the aluminum base alloyof the present invention contains large amounts of silicon from 7 to 20percent. Preferably, the silicon range is from 7 to 12 percent sinceover 12 percent silicon you are in the primary-silicon range and providecoarse silicon particles. Fine, uniform silicon particles, which are inthe 7 to 12 percent range, provide a better product which is easier tocast. Also, the higher silicon contents would tend to detract slightlyfrom elevated temperature strength. This is a significant additive. Asindicated, the silicon is mainly present in the alloy of the presentinvention as dispersed elemental silicon particles. These imparthardness, wear resistance and also tend to lower the coefficient ofthermal expansion. In accordance with the present invention it has beensurprisingly found that the hard particles of silicon can be added tothe alloy while retaining the good elevated temperature propertiesthereof. Furthermore, the basic heat treatability of the alloy of thepresent invention has been found to be unaffected by the siliconadditions in this range. In the 7 to 12 percent range, the silicon ispreferably present in the eutectic form as a uniformly distributeddispersion having a fine particle size. The particle size can becontrolled by controlling the solidification rate to produce the desiredfine particle size, generally by rapid cooling from casting.

The alloy of the present invention contains magnesium in an amount from0.1 to 0.6 percent, and preferably from 0.3 to 0.5 percent. It has beenfound that the magnesium addition is necessary in combination with thecopper in order to obtain appreciable response to heat treatment.

The silver addition is in the amount of from 0.1 to 1.0 percent andpreferably from'0.3 to 0.7 percent. Silver provides a significant extrastrengthening and hardening effect.

The copper addition is in the amount of 3.5 to 6 percent and preferably4.5 to 5.5 percent. The copper addition has been found to provide astrengthening effect. Copper is the principal precipitation hardeningagent,

forming the supersaturated solid solution during solu-' tion heattreatment, from which submicroscopic particles form during artificialaging treatment. The manner and effectiveness of the precipitationprocess is favorably affected by the magnesium and silver additions.

Naturally, numerous additives and impurities may be present in theresultant alloy. Thus, manganese and chromium may be present in amountsup to 0.7 percent and 0.5 percent respectively, generally in an amountof 0.1;to 0.7 percent manganese and 0.1 to 0.5 percent chromium. Eitherof these additives are particularly desirable if iron is present sincethey change the form of the iron from coarse, needle shaped particles torounded or equiaxed particles and lessen brittleness. Iron may bepresent in an amount up to 1.5 percent. If at least 0.5 percent iron ispresent, manganese and/or chromium should be present also as above.Titanium may also be included in an amount from 0.01 to 0.35 percent forcast grain refining, and zinc may be included in an amount up to 0.5percent. Nickel may also be added in amounts up to 2.5 percent to add toelevated temperature stability. Naturally, if desired, any of theforegoing may be present in an amount as low as 0.001 percent. Inaddition to the foregoing, others may be present in an amount up to 0.05percent each, total 0.25 percent.

The alloys of the present invention are particularly useful in themanufacture of pistons for internal combuat'ion engines. Themanufacturers of piston actuated internal combustion engines areconstantly striving to obtain improved performance by reducing theweight of the piston. lnso doing, the piston must have sufficientmechanical strength at operating temperatures and resistance to shapechange. The alloys of the present invention are characterized by highlydesirable elevated temperature properties together with surprisingresistance to galling,'scuffing and wear which would make themespecially suitable for this use.

in addition, however, the alloys of the present invention areparticularly useful for other highly stressed engine parts which operateat elevatedtemperatures, for example, in the new Wankel engines whichare demanding with respect to dimensional stability and resistance towear.

The findings of the present invention are particularly surprising sincewhen large amounts of an additive are incorporated in an alloy systemone would normally anticipate a drastic alteration in thecharacteristics of the basic system. However, in accordance with thepresent invention,'it is surprising that one does not destroy thedesirable characteristics of the matrix alloy, such as heattreatability, elevated temperature properties and high strength.

The alloys of the present invention are cast in the temperature range ofl,250 to l,500 F. They are mainly intended to be cast into approximateshape and machined or ground to final. dimensions. However, otherform'ing operations, such as forging, can be employed. Following castingor forging, the alloy is preferably solution heat treated at 850 to 975F for one to 40 hours, preferably from 900 to 950 F for 12 to hours,followed by quenching into cold or boiling water. This should befollowed by an artificial aging treatment which will develop thestrength and stability that the particular service temperaturesrequirefThe artificial aging is for one to 24 hours at 300 to 500 F. Thesolution heat treatment is particularly preferred as it develops higherproperties.

The alloys of the present invention and improvements thereof will bemore readily apparent from a consideration of the following illustrativeexamples.

EXAMPLE I Several castings were made of the permanent mold (Durville)type from 2,000 gram melts using the following procedure. Melting wasdone in an alumina coated clay graphite crucible, using an inductioncoil for heating. Silicon, copper, magnesium and silver were added inelemental form, others were added as master alloys.

After melting, the melt was fluxed with Cl, gas for ten 7 minutes beforepouring. The mold had a cavity four inches high by four inches wide byone and three quarters inches thick, with a riser on top. The resultantalloys had the compositions set forth in Table 1 below, with the balancebeing essentially aluminum in each case.

TABLE I.ALLOY COMPOSITION Chemical Composition in Weight Percent AlloyNo. Si Cu Mn Mg Ag Fe Ti EXAMPLE II The alloys prepared in Example Iwere all heat treated at 920- F for 16 hours, the temperature was thenraised to 940 F for 6.hours and the materials were water quenched incold water. The resultant properties are shown in 'the following tables.Table [I shows the Brinell hardness of the resultant samples tested immediately after quenching, aged at room temperature for one week and inthe T6 temper. The T6 temper consisted of solution heat treated andquenched material aged at room temperature for 24 hours and then at 310F for 20. hours. Table 111 shows the tensile properties of duplicatemachined round standard tensile specimens in the T6 temper.

TABLE 11 Brinell Hardness Kg/mm Aged EXAMPLE III For comparison, thetensile properties were determined on the following alloy: An aluminumbase alloy containing 0.04 percent silicon, 4.80 percent copper, 0.27percent manganese, 0.46 percent magnesium, 0.61 percent silver, 0.03percent iron, 0.30 percent tivtanium, balance aluminum, said alloybeingidentified as Alloy 6. The alloy was poured from 1350F intopermanent molds of three-fourths inch square section and 7 inch lengthwith a riser along the edge. The material was solution heat treated at985 F for 16 hours, followed by quenching in cold water followed byholding for 24 hours at room temperature followed by treatment for 20hours at 310F. The tensile properties of duplicate specimens are shownin Table IV below.

TABLE IV Tensile Properties A119 Yield Strength Ultimate TensileElongation-% N .fi "?5'411052. L; L 5

6 60.0, 59.9 67.8, 68.2 7.0 and 9.9

TABLE V Brinell Hardness Kg/mm Alloy No. T6 Temper 6 119, 119

Alloy 3, which is the alloy of the present invention, is seen to havehardness and tensile strength properties better than the alloys withoutsilver. In addition, Alloy 3 of the'present invention has higherstrength at room temperature than Alloy 6 which is the standardcommercial alloy even though a lower solution heat treatment was used.This shows that the matrix strength has been retained or enhanced and,therefore, the alloy of the present invention will have correspondinglyhigh strength in elevated temperature service. The tensile elongationnaturally is reduced from that of Alloy 6 because of the hard brittlesilicon particles; however, ductility is not a necessary property forthis type of alloy whereas the improved wear resistance is significant.

Alloy 2, compared with Alloy 1, shows that magnesium is a necessaryaddition in order to obtain response to heat treatment and the high baselevel of strength properties desired. Alloy 4, compared with Alloy 2,shows that manganese which is known to interact with iron, silicon andaluminum to form a hard intermetallic phase, will not compromise thebasic matrix properties. Alloy 5, compared with Alloy 2, shows one canadd the necessary amount of silicon to impart wear resistance for agiven application.

The Brinell hardness data shown in Tables II and V show that hardparticles such as silicon add to the hardness of the alloy, even thoughthe matrix tensile strength is not increased appreciably. Thus, Alloy lwith low tensile strength has comparable Brinell hardness to Alloy 6with high tensile strength. A hardness increase of the type in Alloy 1is significant in terms of wear resistance and galling. Thus, thesuperior Brinell hardness of Alloy 3, the alloy of the presentinvention, is a measure of its enhanced wear resistance when comparedwith standard Alloy 6, as well as when compared with the silver freeAlloys 2, 4 and 5.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

I. An aluminum base alloy consisting essentially of silicon from 7 to 20percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to 1.0percent, copper from 3.5 to 6 percent, balance aluminum.

2. An aluminum base casting alloy having good wear resistance andelevated temperature properties consisting essentially of silicon from 7to 12 percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to 1.0percent, copper from 3.5 to 6 percent, balance aluminum.

3. An aluminum alloy according to claim 2 containing iron in an amountup to 1.5 percent.

4. An aluminum alloy according to claim 3 containing a material selectedfrom the group consisting of from 0.1 to 0.7 percent manganese and from0.1 to 0.5 percent chromium.

5. An aluminum alloy according to claim 2 containing from 0.01 to 0.35percent titanium.

6. An aluminum alloy according to claim 2 containing up to 2.5 percentnickel, up to 0.5 percent zinc, up to 0.7 percent manganese, up to 0.5percent chromium, up to 0.35 percent titanium, up to 1.5 percent iron,others, each up to 0.05 percent, total up to 0.25 percent.

7. An aluminum alloy according to claim 2 in the heat treated condition.

8. An aluminum base casting alloy having good wear resistance andelevated temperature properties for use in pistons and highly stressedengine parts consisting essentially of silicon from 7 to 12 percent,magnesium from 0.3 to 0.5 percent, silver from 0.3 to 0.7 percent,

copper from 4.5 to 5.5 percent; balance essentially aluminum.

9. A process for providing an aluminum base casting alloy having goodwear resistance and elevated temperature properties which comprises:

A. casting an aluminum base alloy consisting essentially of silicon from7 to 20 percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to1.0 percent, copper from 3.5 to 6.0 percent, balance essentiallyaluminum in the temperature range of 1,250 to 1,500 F; and

B. aging said alloy at a temperature of 300 to 500 F for one to 24hours.

10. A process according to claim 9 including the step of solution heattreating after casting but before aging, said solution heat treatingbeing at a temperature of 850 to 975 F for from one to 40 hours.

11. A process according to claim 10 including the step of quenchingfollowing solution heat treating.

2. An aluminum base casting alloy having good wear resistance andelevated temperature properties consisting essentially of silicon from 7to 12 percent, magnesium from 0.1 to 0.6 percent, silver from 0.1 to 1.0percent, copper from 3.5 to 6 percent, balance aluminum.
 3. An aluminumalloy according to claim 2 containing iron in an amount up to 1.5percent.
 4. An aluminum alloy according to claim 3 containing a materialselected from the group consisting of from 0.1 to 0.7 percent manganeseand from 0.1 to 0.5 percent chromium.
 5. An aluminum alloy according toclaim 2 containing from 0.01 to 0.35 percent titanium.
 6. An aluminumalloy according to claim 2 containing up to 2.5 percent nickel, up to0.5 percent zinc, up to 0.7 percent manganese, up to 0.5 percentchromium, up to 0.35 percent titanium, up to 1.5 percent iron, others,each up to 0.05 percent, total up to 0.25 percent.
 7. An aluminum alloyaccording to claim 2 in the heat treated condition.
 8. An aluminum basecasting alloy having good wear resistance and elevated temperatureproperties for use in pistons and highly stressed engine partsconsisting essentially of silicon from 7 to 12 percent, magnesium from0.3 to 0.5 percent, silver from 0.3 to 0.7 percent, copper from 4.5 to5.5 percent; balance essentially aluminum.
 9. A process for providing analuminum base casting alloy having good wear resistance and elevatedtemperature properties which comprises: A. casting an aluminum basealloy consisting essentially of silicon from 7 to 20 percent, magnesiumfrom 0.1 to 0.6 percent, silver from 0.1 to 1.0 percent, copper from 3.5to 6.0 percent, balance essentially aluminum in the temperature range of1,250* to 1,500* F; and B. aging said alloy at a temperature of 300* to500* F for one to 24 hours.
 10. A process according to claim 9 includingthe step of solution heat treating after casting but before aging, saidsolution heat treating being at a temperature of 850* to 975* F for fromone to 40 hours.
 11. A process according to claim 10 including the stepof quenching following solution heat treating.